We have shown that i.v. infusion of norepinephrine (2 micrograms/min/kg for 90 min.) produces a marked myocarditis in the rabbit within 48 hours. The severity of myocardial damage is significantly reduced in rabbits pretreated with insulin, 10 U/kg or 5 U/kg, but not with 1 U/kg. Additional animals will be prepared to complete the insulin dose response relations under this protocol. Histologic evaluation will be supplemented by CPK enzyme measurements in each preparation. Additional rabbits will be prepared and similarly studied and sacrificed after 3 weeks. Myocardial scarring will be assessed histologically and by hydroxyproline determinations. Preliminary studies will be undertaken to generate a model for catecholamine cardiomyopathy in the newborn piglet and lamb. The animals will be anaesthetized with pentobarbital (30 mg/kg). Heart rate, arterial pressure, PO2, pH and glucose concentration will be determined. NE will be infused i.v., as mentioned. After 48 hours the animals will be sacrificed and the hearts examined by the techniques described. Similar studies will be performed in animals rendered diabetic by alloxan administration. Circulating insulin levels will be measured. The protocol is designed to test the hypothesis that insulin deficient animals will manifest greater sensitivity to catecholamine cardiomyopathy. BIBLIOGRAPHIC REFERENCES: Downing, S.E., J.C. Lee and R.P. Rieker. $ Mechanical and metabolic effects of insulin on newborn lamb myocardium. Am. J. Obstet. Gynecol. 127: 649-656, 1977. Nudel, D.B., J.C. Lee and S.E. Downing. Reciprocal inhibition of cardiac responses to norepinephrine and insulin. AJP 1977, in press.